Human renal kallikrein and prokallikrein have been purified and separated by immunoaffinity chromatography; affinity chromatography on immobilized basic pancreatic trypsin inhibitor (Trasylol), lily bulb trypsin inhibitor, and Concanavalin A; gel filtration; and hydroxyapatite chromatography. The proenzyme after trypsin activation has a specific activity of19 TAMe units (TU)/A280, while our purest actove emzyme has a specific activity of 45 TU/A280. Evidence is presented that pure active enzyme will have a specific activity of 59-60 TU/A280. A potent new inhibitor of human polymorphonuclear (PMN) leukocyte elastase has been obtained from calla flower bulb extracts. The only partially purified calla bulb inhibitor (Mr=33,000 and pI=5.3) is a much better inhibitor of this elastase than previously reported trypsin inhibitors from soy beans, lima beans, and pancreas, and also does not inhibit pancreatic elastase.